The teachings presented herein relate generally to stereoscopic images. More specifically, the teachings presented herein relate to the creation of moiré-based auto-stereoscopic watermarks in rendered images.
The principle of stereoscopic vision is well understood. At the most basic level, each of the viewer's two eyes must perceive the subject matter to be viewed from a slightly different perspective. That is to say that, although the differences are generally quite subtle, each eye receives a different image.
Several methods are commonly used to produce stereoscopic images. On the one hand, these include the use of direction selective screens onto which two or more images may be projected simultaneously. Depending on the viewer's position, a different image may be observed by each eye. Where only two images are required, it is common practice to use polarizing techniques. Each image is projected with a characteristic polarization and when viewing through complementary polarizing viewing spectacles, each eye only sees the picture intended for its reception.
Most existing methods to view printed stereoscopic images require either special glasses (colored or polarized) or lenticular lenses. The stereogram may be the one exception which does not need any special viewing aid; however, many people find that it is very difficult and uncomfortable to see the hidden stereo image. Lenticular lenses are common but incur some additional expense and complexity as they require an embossed transparent material for operation.
With most current digital watermark technologies, to retrieve embedded watermark information from printed documents requires scanning and processing by a scanner and a computer. It is desirable to provide a simple and quick way to provide invisible watermarks embedded in documents. It is desirable to provide these invisible watermarks with means that will quickly make them visible in a given print item, where an observer is provided only with a simple overlay without the need for lenticular or other special lenses, and for which this means is readily and inexpensively generated with common materials using conventional printing apparatus.
Disclosed in embodiments herein is a moiré-based auto-stereoscopic watermark system. The watermark system comprises a substantially transparent substrate having a first side. As applied to and placed on the first side of the substantially transparent substrate is a first side applied marking material of periodic structure having a first frequency. The watermark system further comprises a second substrate. As applied to the second substrate is a second side applied marking material which further comprises a first partition and a second partition, the first partition having a periodic structure at a second frequency, that second frequency being related to but some delta away from the first frequency. The second partition has a periodic structure at a third frequency, that third frequency being related to but some delta away from the first frequency, such that when the substantially transparent substrate is placed upon the second substrate in substantial alignment with the second side applied marking material, a moiré-based auto-stereoscopic watermark image is evident to an observer.
Further disclosed in embodiments herein is an alternate moiré-based auto-stereoscopic watermark. The watermark includes a substantially transparent substrate having a first side applied marking material having a periodic structure at a first frequency, as applied to and placed on at least one side of the substantially transparent substrate. The watermark also includes an additional substrate having a selected side, and a second side applied marking material as applied to the selected side of the additional substrate. The second side applied marking material further comprises a first partition and a second partition, the first partition having a periodic structure at a second frequency, that second frequency being related to but some delta away from the first frequency, and the second partition having a periodic structure at the first frequency. The above are arranged such that when the substantially transparent substrate is placed upon the additional substrate in substantial alignment with the second side applied marking material a moiré-based auto-stereoscopic watermark image is made evident to an observer.
Further disclosed in embodiments herein is a method for providing a moiré-based auto-stereoscopic watermark imaging system, by applying marking material with a halftone periodic structure at a first frequency to a substantially transparent substrate. The method further comprises applying marking material within a first partition on a selected side of a second substrate with a halftone periodic structure at a second frequency, that second frequency being related to but some delta away from the first frequency. The method also comprises applying marking material within a second partition on the selected side of the second substrate with a halftone periodic structure at a third frequency, that third frequency being related to but some delta away from the first frequency. This is followed by placing the substantially transparent substrate upon the second substrate in substantial alignment with the selected side applied marking materials such that a moiré-based auto-stereoscopic watermark image is evident to an observer.